Roller cone drill bit

ABSTRACT

A roller bit for use with a drill string, having at least two cutters which are generally conically shaped; each cutter includes one or more teeth in inclined planes across a conical surface. The bit is attached to the drill string with the axis of rotation of the cutter angled with respect to the longitudinal axis of the drill string. The teeth on each cutter are arranged for maximum cuttings size and penetration rate.

This is a continuation of application Ser. No. 143,340, filed Apr. 24,1980 now abandoned.

DESCRIPTION

1. Technical Field

This invention relates in general to rotary drills for deep-welldrilling and, in particular, to an improved drill bit having teethproviding improved shearing and crushing action.

2. Background of the Prior Art

In general, equipment for drilling wells and for mining dates back manycenturies. Of late, such drilling equipment comprises a rotary drillstring which is stabilized in the hole being drilled. The drill bititself is on the end of this rotating shaft and, by its rotating action,cuts through the rock or other strata in which the hole is being made.Drilling fluid, usually air or mud, is circulated through the rotarydrill string cooling the drill bit, simultaneously purging the corebottom. U.S. Pat. Nos. 3,302,983 and 3,659,663 show various means forstabilizing the rotary drill string within the bore, while U.S. Pat.Nos. 959,539; 1,143,272; 1,860,587 and 2,169,640 show various drill bitstructures which may be utilized in boring a hole. When consideringpentration rate, the method in which the formation is stressed isimportant. Traditionally, the rolling cutter rock bit penetrates aformation by applying a vertical pressure until it yields. The formationis stressed by a series of individual circumferentially-spaced teeth.However, it would also appear important to develop a stress sequencethat not only stresses the formation vertically but laterally as well.Other factors which should be considered in increasing the efficiency,and thus the penetration rate of a drill bit, in addition to lateralpressure intensities, is the self-cleaning capability, or lack thereof,of the bit or cutter, and the capability of the bit to overcomeformation strength. Other factors which are important to the structureof an effective drill bit will become apparent and are discussed below.

Therefore, an object of the subject invention is a rotary drill bitwhich can efficiently cut through rock with a high rate of penetration.

An additional object of the subject invention is a rotary drill bit inthe shape of a cone having teeth of such a structure and relationship toone another that the penetration rate is greatly enhanced.

Yet another object of the subject invention is a drill bit which isself-cleaning during the drilling function.

Still another object of the subject invention is a roller drill bithaving teeth shaped and spaced in a precise relationship for increasedpenetration rate and maximum cutting size.

SUMMARY OF THE INVENTION

These and other objects are attained in accordance with the presentinvention wherein there is provided a roller drill bit comprising tworoller cone cutters which rotate on axes substantially perpendicular toone another. Each roller cutter or cone is generally frustoconical inoverall shape, with a plurality of irregularly-spaced and inclinedteeth. The teeth on each roller cutter are complementary, each having alead tooth extending from the base to the apex of the roller conecutter. In addition, the spacing between adjacent teeth increases as thecross-sectional area of the cone roller bit decreases. The respectivecones are also tapered differently, aiding in the creation ofdissimilar, but complementary, teeth patterns on each cone rollercutter. The teeth on each roller cone cutter are formed in planes which,viewed in cross-section along its axis of rotation, are intersecting,adding to the crushing and shearing action of the roller bit inoperation.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF DRAWINGS

The foregoing and other objects, features and advantages of thisinvention will become apparent from the following more particulardescription of embodiments of the invention as illustrated in theaccompanying drawings wherein:

FIG. 1 is a perspective view of a rotary drill string utilizing therotary drill bit of the subject invention;

FIG. 2 is a perspective view of a rotary drill bit of the subjectinvention;

FIG. 3 is a perspective view taken along line 303 of FIG. 2 showing theteeth pattern of one rotary cone of the subject invention;

FIG. 4 is a perspective view of another rotary cone of the subjectinvention taken along line 4--4 showing its tooth pattern;

FIG. 5 is a cross-sectional view of the rotary cone of FIG. 3 along theline 5--5 showing the intersecting planes of the teeth of the rotarycone;

FIG. 6 is a cross-sectional view of the rotary cone of FIG. 4 showingthe intersecting planes of the teeth of the rotary cone.

DETAILED DESCRIPTION

Referring now to FIG. 1, there is shown a drill string 10 having acentral shaft 20 which is stabilized for rotation by stabilizer rollersor the like as known in the art. Secured to the end of the shaft 20 isroller bit assembly 15. Rotatably mounted on the roller cone bitassembly 15 are individual cone cutters 25 and 35.

As can be better seen in FIG. 2, cutters 25 and 35 are each rotatablymounted on ears 32 and 33, respectively, through bearings mounted onseats 24 and 34 within the cone cutters. The axes of rotation of theroller cones lay approximately at a 90° angle to one another and atapproximately 45° angles to normal. In the mid-portion of the roller bitassembly 15 and to either side of the roller cones are cooling fluidinjection ports 30 for injecting a cooling fluid such as mud or the likefor cleaning the teeth of the rotary cone bits, facilitating circulationand carrying the cuttings up and away from the bottom of the hole.

Each roller cone cutter has a configuration different from the other,although all have teeth of large size having both a large pitch and alarge depth.

In particular, roller cone cutter 25, shown in FIGS. 3 and 5 has majorteeth 26, 27 and 28. The planes 26a, 27a and 28a of each tooth aregenerally at inclined angles to a plane P1 that extends from the apex 29of the roller cone cutter 25 to the center of the base of the cone. Thegeneral curvature of each tooth obscures much of the pattern of suchinclined planes which, while generally in an upward direction towardsthe apex of the cone, constantly varies its degree of inclination,thereby yielding greater penetration rates, as will be discussed. Inother words, each of the general tooth planes intersects with the otherswhile the tooth contour varies within the plane. A tooth pattern iscreated in this manner which forms a cutting structure for formationloading which may be constant in vertical pressure intensities yetvaried in lateral pressure intensities.

Roller cone cutter 35, shown in FIGS. 4 and 6, has teeth which are alsoat inclined angles to the plane P2 that extends from the apex of theroller cone cutter, generally shown at 39, to the center of the base ofthe cone. Each of these planes are intersecting and, in addition, theangle of the inclined planes are in continuous change as the planetransverses the face of the cone as a result of the irregularfrustoconical shape of the cone and the shape of the tooth itself.

Roller cone cutter 35 also has three teeth 36, 37 and 38, one of which37 is the lead tooth. Lead tooth 37 is the longest tooth on the cone 35and also has a greater number of inclined plane combinations or changes.These plane angle changes of lead tooth 37 are complimentary, notidentical, to the plane angle changes of the lead tooth 27 of rollercone cutter 25. This relationship is true for each tooth on opposingroller cone cutters. As a direct result of such complementary planeangles, in cutting through a rock formation, no tooth of either rollercone cutter ever hits a rock formation at the same angle as a followingtooth. Thus, consecutive elongated craters inflicted on the rockformation will always be intersecting, creating an environment in whichthe formation can yield to the lateral forces that are simultaneouslyexerted upon it, therefore, increasing the rate of rock failure.

Contributing to the disparate planes in the roller cone cutters 25 and35 is the fact that the cones themselves of the roller cone cutters haveunequal tapers; further, as the area of the cone decreases, the spacingbetween the teeth increases. Further, as the area of the cone decreases,that is, as the teeth move toward the apex 29 of the cone, the spacingbetween the teeth increases. This increase is shown, for example, inFIG. 4 where V1 represents the distance or spacing between tooth 27 andtooth 28 at a first point relative to apex 29 and where V2 representsthe distance between the same tooth 27 and the same tooth 28 at a secondpoint closer to apex 29. Thus, the problem associated with rock cuttingsmigrating toward the center or apex of the cutter and compacting andplugging the teeth at the point is alleviated. The teeth actuallydiverge as they cross the face of the cone and, therefore, the cuttingswill not migrate toward the center of the roller cone cutter and therewill be no compacting of the rock material at that point or the areaabout the center.

In addition to the increased spacing of the teeth as they near the apex,the teeth wedge angle A (inside face angle which is the angle formedbetween the tooth plane or tooth face, such as 27a, and a line x drawnperpendicular to plane P1 through the base point 27x of tooth plane 27a,as shown in FIG. 5) also increases to compensate for the rapid increasein the inclined plane of the tooth as it nears the bit apex. The greatertooth wedge angle reduces the shearing action and increases crushingaction of the tooth, all for maximum cuttings size and increasepenetration rate. Thus, the wedge angle A of a tooth will change, as at27, where the tooth appears to climb to the apex of the cone. In apreferred embodiment, a tooth may end abruptly as at 16 and 17, furthercontributing to the discontinuous nature of the rotary cone bit of thesubject invention.

Another benefit of the increase in the tooth spacing toward the centerof the cutter is a larger cuttings size, that is, the roller cone cuttercan take a larger bite out of the formation material being penetrated.With such a larger bite, the penetration rate can be greatly increased.

As stated above, not only does the inclined plane as illustrated byplanes 27a and 28 a intersecting at B of each tooth intersect and thespacing between the teeth increase, but also the plane of each tooth ona roller cone bit continually changes. As a result of such intersectionsof the planes and variations in the tooth spacings, the lateral pressureintensities exerted by the teeth fluctuate, thereby increasing thecuttings obtained through the rotation of the roller cone cutter. Statedanother way, the teeth do not contact the formation material in the sameplace at the same intensity or load. Thus, a tooth may bear down on aformation material along a certain plane, simultaneously movinglaterally for a greater stressing and yielding of the formationmaterial. As the roller cone cutter rotates, it will contact the sameformation material on an intersecting plane and also in a manner inwhich the tooth contacting the formation material will move laterally toincrease the formation stressing and yielding. As the roller drill bitassembly rotates bringing the respective roller cone cutters intocontact with different formation material with each rotation of thedrill bit, the formation material is cratered in each pass of the rollercone cutter from a different angle, thereby increasing the penetrationrate and breaking up the formation material with the maximum cuttingssize.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thevarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out the invention, but that the invention willinclude all embodiments falling within the scope of the appended claims.

I claim:
 1. A roller bit for use with drilling strings in thepenetration of earth, as in drilling through rock formations, saidroller bit comprising first and second roller cone cutters, each of saidroller cone cutters formed in a generally conical configuration andhaving a base and an apex, said first roller cone cutter revolvingaround a first axis, said second roller cone cutter revolving around asecond axis, said first and said second roller cone cutters each havinga plurality of teeth extending in planes about the perimeter of each ofsaid roller cone cutters, said teeth extending generally from the basetoward the apex of each of said roller cone cutters, the spacing betweenadjacent teeth on the same roller cone cutter increasing as saidadjacent teeth extend from said base of said roller cone cutter towardsaid apex thereof, thereby allowing larger cuttings and increasedcleaning action of said cutter.
 2. The roller bit of claim 1 wherein theplanes of inclination of each tooth of each roller cone cutter iscontinuously varied.
 3. The roller bit of claim 1 wherein the insideface angle of said teeth increases as the cross-sectional area of theroller cone associated with said teeth decreases.
 4. A drill stringassembly for drilling of deep holes in rock and other materials, saidassembly including a drill string, a bit assembly mounted on a lower endof said drill string, a first and second roller cone cutter on said bitassembly, said first roller cone cutter revolving about a first axis,said second roller cone cutter revolving about a second axis, said firstand said second roller cone cutter each having a plurality of teethextending in planes about the face of said roller cone cutter, each ofthe planes of said teeth of said roller cone cutters varying in theinclination of said planes, thereby providing for increased lateralstress on the rock formation.
 5. The drill string assembly of claim 4wherein said teeth of said first roller cone cutter and said secondroller cone cutter are different in size, pitch and spacing and extendin different planes across the face of said roller cone cutters.
 6. Thedrill string assembly of claim 4 wherein each of said roller conecutters has a plurality of teeth extending around the perimeter of saidroller cone cutter and adjacent teeth of each roller cone cutter have anincreasing spacing between them as they move from the base toward theapex of an associated roller cone cutter.
 7. The drill string assemblyof claim 1 wherein each of said teeth extending in planes about the faceof said roller cone cutters intersect one another for subjecting therock formation to varied patterns of stress when drilling.